一道面试题，简单模拟spring ioc

Posted 2020-08-09

自己实现的，程序写的土了点，很多情况没去考虑，主要是复习理解怎么使用反射来实现spring 的依赖注入。

 

 

 

 

package dom4jtest;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class Test3 {
    private static Object o1;
    public static void main(String[] args) {
        BeanA ba = (BeanA) getBean("beanA");
        ba.getBeanB().show();
    }
    public static Object getBean(String name){
        if(o1==null)
            o1 = setBean(name);
        return o1;
    }
    @SuppressWarnings("unchecked")
    public static Object setBean(String name){
        SAXReader sr = new SAXReader();
        Object o = null;
        Class clz = null;
        Class clz2 = null;
        String ref = null;
        String name1 = null;
        try {
            Document doc = sr.read(Test3.class.getClassLoader().getResourceAsStream("beans.xml"));
            Element e = doc.getRootElement();
            @SuppressWarnings("unchecked")
            List<Element> eles = e.elements();
            for(Element ee : eles){
                if(ee.attributeValue("id")!=null){
                    if(ee.attributeValue("id").equals(name)){
                        clz = Class.forName(ee.attributeValue("class"));
                        o = clz.newInstance();
                    
                        List<Element> elus = ee.elements("property");
                        ref = elus.get(0).attributeValue("ref");
                        name1 = elus.get(0).attributeValue("name");
                        if(ref!=null&&name1!=null){
                            for(Element eee:eles){
                                if(eee.attributeValue("id")!=null){
                                    if(eee.attributeValue("id").equals(ref)){
                                        clz2 = Class.forName(eee.attributeValue("class"));
                                        name1 ="set"+ name1.substring(0, 1).toUpperCase() + name1.substring(1);
                                        Method m = clz.getDeclaredMethod(name1,clz2);
                                        m.invoke(o, clz2.newInstance());
                                    }
                                    
                                }
                            }
                        }
                        
                    }
                }

            }
        } catch (DocumentException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e1) {
            e1.printStackTrace();
        } catch (InstantiationException e1) {
            e1.printStackTrace();
        } catch (IllegalAccessException e1) {
            e1.printStackTrace();
        } catch (IllegalArgumentException e1) {
            e1.printStackTrace();
        } 
        catch (InvocationTargetException e1) {
            e1.printStackTrace();
        } catch (NoSuchMethodException e1) {
            e1.printStackTrace();
        } 
        catch (SecurityException e1) {
            e1.printStackTrace();
        }
        return o;    
    }
}